1. Field of the Present Invention
The present invention generally relates to a self-ignition type internal combustion engine that has a supercharger with a cooling device for cooling intake air from the supercharger, and that utilizes the compressive action of a piston to cause an air-fuel mixture in a combustion chamber to self-ignite and combust.
2. Background Information
As a highly efficient low-emissions gasoline internal combustion engine, a self-ignition type internal combustion engine with a high compression ratio has been proposed which achieves low NOx and high efficiency resulting from lean burning by combusting a pre-mixture using compression self-ignition combustion. This self-ignition type internal combustion engine has a narrow load range in which it can be operated. More particularly, in order to secure a region in which the engine rotational speed and engine load are both high, it is necessary to use supercharging to maintain the operable range.
As seen in FIG. 18, an explanatory graph is illustrated showing the operating region for which self-ignition combustion is possible when the supercharging pressure is constant. In FIG. 18, region (I) is without supercharging, region (II) is with supercharging, and region (III) involves cooling the intake air after supercharging to the minimum temperature for which ignition is possible. When these regions are compared at a constant supercharging pressure, the maximum load range, for which operation is possible, declines as the engine rotational speed increases. However, since supercharging is conducted in regions (II) and (III), the maximum load range for which operation is possible is higher in these regions than in region (I).
The high load limit side of the operating load is limited by knocking; this knocking is defined by the mixture ratio of the air-fuel mixture, e.g., the value obtained by dividing the amount of air by the amount of fuel. Therefore, since the operating load range is expanded, it is possible to cool the intake air, whose temperature was raised by supercharging, to a temperature for which compression self-ignition can be conducted and increase the amount of air introduced into the combustion chamber.
Due to the characteristics of the supercharger, the maximum supercharging pressure and the amount of intake air both increase as the engine rotational speed increases. When the maximum supercharging pressure of the supercharger is used, the operable range is shown in FIG. 19. Here, regions (I), (II), and (III) correspond to regions (I), (II), and (III) in FIG. 18. The maximum load range for which operation is possible in regions (II) and (III) (where supercharging is conducted) is higher than in FIG. 18. In particular, region (III) (where the intake air is cooled after supercharging) allows operation in a higher load range than in region (II) (where knocking occurs in section A when the, temperature is high). However, when the intake air is merely cooled after supercharging, there are operating regions where the temperature of the intake air is too low and self-ignition operation is not possible. Thus, there is room for improvement.
Japanese Laid-Open Patent Publication No. 11-210477 discloses an internal combustion engine that attempts to prevent overcooling of the intake air. Specifically, this publication proposes providing a bypass passage that bypasses the inter-cooler that cools the intake air after supercharging and controls the temperature of the intake air by passing all of the post-supercharging intake air through the bypass passage during warming up and low-load operation, at which times operation is stratified.
Japanese Laid-Open Patent Publication No. 11-210539 discloses an internal combustion engine in which the temperature inside the combustion chamber is detected by using a temperature sensor installed in the intake port, the EGR gas amount is controlled, and the opening timing of the intake valve is controlled. In this way, the temperature of the gas inside the combustion chamber is held at a temperature for which self-ignition will occur when assist ignition is conducted using a spark plug.
In view of the above, there exists a need for an improved internal combustion engine that utilizes the high efficiency and low emissions of compression self-ignition combustion to the maximum degree and that secures an operable range up to high load regions. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
In order to utilize the high efficiency and low emissions of compression self-ignition combustion to the maximum degree and secure an operable range up to high load regions, it is necessary to execute control such that the intake air introduced into the combustion chamber is brought to the optimum temperature state in response to the operating conditions at the time, i.e., the engine rotational speed and required load.
However, while the inventions described in the aforementioned publications control the intake air temperature or the temperature of the gas inside the combustion chamber, they do not control to the temperature state that is optimum with respect to the aforementioned operating conditions necessary for compression self-ignition combustion. Consequently, it is not possible to expand the operating load range of compression self-ignition combustion.
Therefore, the purpose of the present invention is to control the temperature of the intake air so as to expand the operating load range of compression self-ignition combustion.
In order to achieve the aforementioned purpose a self-ignition internal combustion engine is provided that comprises a combustion chamber, a supercharger, a cooling device, a cooling bypass path, a cooling bypass flow rate valve and a controller. The combustion chamber has an intake passage, an exhaust passage and a piston in the combustion chamber for compressive action to cause an air-fuel mixture to self-ignite and combust. The supercharger is connected to the intake passage upstream of the combustion chamber. The cooling device is located in the intake passage between the supercharger and the combustion chamber to cool intake air from the supercharger. The cooling bypass path has an inlet and an outlet with the inlet fluidly coupled to the intake passage between the supercharger and the cooling device and the outlet fluidly coupled to the intake passage between the cooling device and the combustion chamber. The cooling bypass flow rate valve is arranged to regulate an opening to adjust an amount of intake air that passes through the cooling bypass path. The controller is operatively coupled to the cooling bypass flow rate valve to control the opening of the cooling bypass flow rate valve based on operational conditions of the combustion chamber to perform self-igniting combustion.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.